Sandbian Age Research Articles

Stratigraphic age of the Ordovician sedimentary succession in Lumparn Bay, Åland Islands, Finland

ABSTRACT The depression of the ancient Lumparn meteorite impact structure is partly infilled by Cambrian and Ordovician sediments, lying nowadays below the seawater. The Ordovician carbonate succession at this site, recognised through erratic boulders and by the drilling project in the late 1950s, is of particular interest due to its isolated and distant location from other areas with Ordovician sediments in the Baltoscandian Palaeobasin. In this study, we present new data on ostracod biostratigraphy and stable carbon isotope chemostratigraphy obtained from three old drillcores. Comparison of ostracod distribution with sections in Estonia generally supports the previous interpretations of a Darriwilian and Sandbian age for the lowermost Tranvik Limestone (which we propose renaming the “orthoceratite limestone” in the Åland Islands area). The uppermost Östersjö Limestone spans almost the entire Katian age. We also observe the global MDICE and GICE carbon isotopic excursions, as well as Katian Rakvere and Saunja excursions, within the Lumparn succession. The Ordovician succession in Lumparn Bay is facially resembling the Estonian Shelf facies of the Baltoscandian Palaeobasin.

High diversity and early radiation of organic-walled phytoplankton in southern Baltica during the Middle-Late Ordovician – evidence from the Borenshult-1 drillcore of southern Sweden

ABSTRACT Highly diverse and well preserved organic-walled phytoplankton were recorded from the Darriwilian–early Katian interval of the Borenshult-1 drillcore. We identified 154 species in 53 genera, and three assemblages were distinguished; Assemblage A of a late Darriwilian age, Assemblage B of a Sandbian age (further subdivided into sub-assemblages B1 and B2), and Assemblage C dated as Katian. Taxa with “Silurian affinities” with previous first appearance datum in the early Silurian, Hirnantian, such as Metaleiofusa and Visbysphaera, are here recorded from the late Darriwilian and Sandbian respectively. These occurrences question the relationship between the appearance of pioneering phytoplankton morphotypes and the Hirnantian glaciation. Other taxa with no pre-Silurian records such as Visbysphaera pirifera subsp. minor, Petaloferidium cazurrum and Dorsennidium cf. D. estrellitae are here present in the Sandbian, where bentonite beds are intercalated. The diversity curve of acritarchs shows similarities with those proposed for the Darriwilian-Katian of Baltica with main differences in the interval with bentonite beds representing an intense volcanic activity. The species Metaleiofusa arcuata Wall is here emended and a new combination is proposed: Petaloferidium cazurrum (Cramer) comb. nov. The genus Fankea is recorded for the first time from Swedish strata, suggesting a dominant high- to middle latitudinal distribution instead of a Perigondwanan distribution. We contend that the location of paleo-southern Sweden contributed to the great diversity seen, since a middle-low latitude provided a suitable habitat with warm, shallow water, rich in nutrients.

Middle–Late Ordovician brachiopods from Ningnan, southern Sichuan Province, Southwest China: Implications for macroevolution and palaeogeography

Middle to Late Ordovician brachiopods from the Huadan Formation (upper Darriwilian–Sandbian) of Ningnan County, southern Sichuan Province, are systematically documented here for the first time. The locality belongs to the western margin of the Upper Yangtze Platform, South China palaeoplate, and the brachiopod fauna includes one new genus and three new species as well as five other constituents: Hingganoleptaena sp., Acculina zhongliangziensis n. sp., Ningnanmena longisepta n. gen. n. sp., Kassinella (Trimurellina) minuta n. sp., Lepidorthis typicalisWang, 1955, Protoskenidioides weixinensisZhan and Jin, 2005, Porambonites transversusXu, Rong and Liu, 1974, and Psilocamerella sp. Taxonomically it is a typical representative of a Middle to early Late Ordovician brachiopod fauna, and, together with some other evidence from other fossil groups like trilobites, conodonts, chitinozoans, a late Darriwilian–Sandbian age could be inferred for the horizon yielding this fauna. According to the richness of each constituent, this fauna is suggested to be called the Acculina-Ningnanmena fauna (ANF). Numerical palaeogeographical analysis shows that two broad palaeobiogeographic provinces could be recognized during this particular time interval, and, although the ANF is grouped into the South China cluster, it shares very little similarity with other representatives of that group except for two cosmopolitans. It further confirms that the Great Ordovician Biodiversification Event (GOBE), in other words the Ordovician radiation, was actually manifested by the strong localization of major marine organisms such as brachiopods, trilobites, graptolites, etc.

Age and significance of the Fire Bay assemblage: an Ordovician arc fragment within the Clements Markham belt, northwestern Ellesmere Island, Canada

The Fire Bay Formation of Trettin (1998), Clements Markham belt, Ellesmere Island, Canada, includes volcanic rocks described as Silurian in age based on Llandovery graptolites in adjacent clastic rocks. New field observations suggest the Llandovery fossils are from packages of the Silurian Danish River and/or Lands Lokk formations that are fault-bounded rather than stratigraphically tied to Ordovician sections that contain a 470.0 ± 0.2 Ma lithic tuff, volcaniclastic units with maximum depositional ages (MDAs) of 466 ± 2 and 462 ± 2 Ma based on detrital zircon, volcanic clasts with ages of 498 ± 6, 478 ± 4, and 477 ± 8 Ma, and Ordovician conodonts and graptolites of Darriwilian and Sandbian age, respectively. Since the Fire Bay Formation of Trettin (1998) lacks a type section and is fault-bounded with ambiguous age relationships, Ordovician volcanic units and fault-bounded clastic rocks correlated with the Hazen Formation are both included in the Fire Bay assemblage following the original interpretations of Trettin and Nowlan (1990). The Fire Bay assemblage records juvenile Ordovician arc magmatism proximal to the Pearya terrane. The adjacent Lands Lokk Formation yields bimodal age peaks at 440–430 and 465 Ma, MDA of 424 ± 3 Ma, and εHf(t) values of −5 to +10. The signature matches Ordovician Pearya units and Silurian circum-Arctic arc sources but there is no evidence for Silurian arc magmatism between the Pearya terrane and Laurentian margin, compatible with Pearya accretion during oblique Ordovician arc collision and Silurian sinistral translation along the northern Laurentian margin.

Late Sandbian (Sa2) radiolarians of the Pingliang Formation from the Guanzhuang section, Gansu Province, China

AbstractA diverse, well-preserved radiolarian assemblage is reported from the Sandbian age Climacograptus bicornis Graptolite Biozone. This new assemblage, recovered from the Pingliang Formation in the Guanzhuang section, China, includes six new species along with 13 other previously described taxa. Geminusphaera new genus incorporates G. grandis n. sp. and G. kongtongensis n. sp. and is proposed for inaniguttids constructed from two distinct porous spheres bearing seven or more primary spines. Protopylentonema new genus is introduced to incorporate pylomate entactinarians with five-rayed initial spicules. It includes P. ordosensis n. sp. as well as P. aperta, P. rimata, and P. insueta that were formerly assigned to Kalimnasphaera. Micro-computed tomography investigation of skeletal microstructure supports establishment of the new genera together with other new spumellarian species: Haplotaeniatum implexa n. sp., Inanigutta quadrispinosa n. sp., and Kalimnasphaera pingliangensis n. sp. It also indicates that family-level reassignment of Etymalbaillella from the Proventocitidae to the Ceratoikiscidae is appropriate.Global distribution of Late Ordovician radiolarian occurrences highlights a strong preference for areas with equatorial to tropical sea surface temperatures. This must have led to ecological stress among radiolarian communities in adapting to global cooling in the Hirnantian.UUID: http://zoobank.org/3d3f55b8-0e70-4f9f-9738-265750d8ec3a.

Paleo-environmental changes during the Middle–Late Ordovician transition on the Yangtze Platform, South China and their ecological implications

Rocks of Darriwilian and Sandbian age (Middle–Late Ordovician) record the extraordinary peak of the Great Ordovician Biodiversification Event (GOBE) and significant global environmental changes. To track paleo-environmental changes through this critical time, we have analyzed iron speciation, trace elements and total organic carbon in samples of the Miaopo Formation from an intra-shelf basin in South China. The results reveal moderate primary productivity and possible fluctuations in benthic redox. Upwelling during marine transgression is thought to have increased the availability of nutrients in surface waters, sustaining the biological pump. Enhanced export of organic matter would have consumed dissolved oxygen at depth, driving the system toward anoxia. However, it is also possible for deep-water renewal events to transfer more dissolved oxygen into the bottom water. Those proxies suggests high primary productivity and varying sea level (global and local), not benthic anoxia, as the driver of accumulated “black shale”. Thus, the local marine ecosystem thrived in this oxic intra-shelf basin, challenging the preexisting paradox that the high-diversity community flourished in an oxygen-depleted environment.

Кокчетау-Иссыккульский террейн Казахстанского палеоконтинента и его палеоширотное положение в ордовике

Research subject. The Kazakhstan (Kazakh-Kyrgyz) paleocontinent attracts much research attention. In this article, we present data on the tectonic structure of the Early Paleozoic Kokchetau-Issykkul sialic terrain. Materials and methods . The geodynamic position of the Kokchetau-Issykkul terrain was determined by analysing samples of Ordovician rocks collected across 11 sites using the paleomagnetism method. Thus, we studied the paleomagnetism of red sandstones, siltstones, tuffaceous siltstones and basalts, as well as that of andesite and tuffaceous rocks in marine sediments, which affiliation to different Ordovician formations was established on the basis of trilobite, brachiopod, conodont and graptolite fauna. Results. Early Paleozoic rocks are exposed in the northern part of the studied terrain (Kokchetau district) and in the Issyk-Kul region, which covers southern Kazakhstan, northern Kyrgyzstan and western Xinjiang. The sutures of Chistopol-Terskei and Iradir-Ili ocean basins serving as the boundaries of the Kokchetau-Issykkul terrain are located in the allochthonius position. A multi-storey system of napes composed of pre-Paleozoic and Early Paleozoic rocks of the oceanic crust, volcanic oceanic island arcs and continental slope were studied near the Terskei margin of the terrain. This system of napes is covered by sediments containing graptolites of the Floian-Darriwilian age. Subduction-related volcanism near this margin of the terrain is of the Darriwilian and Sandbian age, while I-type granites are of the Darriwilian age. The over-thrusting of the Iladyr-Ili oceanic crust on the Ili border of the terrain also occurred in the middle Ordovician. Subduction-related mag-matism occurred here in the Late Darriwilian and Sandbian periods. Conclusion. The conducted studies testify to the geodynamics of the region. In the Early and Middle Ordovician, the Kokchetau-Issykkul terrain was a sialic volcanic arc separated from other sialic terrains by ocean basins. In the Middle Ordovician, the counter subduction of the oceanic crust under the Kokchetau-Issykkul island arc occurred. This process led to the closure of the Chistopol-Terskei and Iradir-Ili ocean basins in Middle Ordovician and to the formation the Kazakhstan continent by the collision of the Early Paleozoic sialic terrains and oceanic island arcs. According to the study of the paleomagnetism of Ordovician rocks in the Kokchetau-Issykkul island, the position of the middle part of this arc is determined to be at the paleogeographic latitude of 9.1 ± 5.4°.

Graptolite biostratigraphy of the Ordovician Almelund and Sularp Shale formations of the Fågelsång-3 drill core, Scania, Sweden

ABSTRACTThe upper Middle to basal Upper Ordovician succession (Darriwilian to Sandbian) of the Fågelsång-3 drill core provides new important information on the graptolite biostratigraphy of Scania, southern Sweden. The Scanian succession is known largely from drill cores and a few scattered outcrops exposing only parts of the interval. The Darriwilian Almelund Shale Formation overlies the Komstad Limestone Formation and has a thickness of more than 42 m in the Fågelsång-3 drill core. A seemingly complete succession through the Holmograptus lentus, Nicholsonograptus fasciculatus, Pterograptus elegans, Pseudamplexograptus distichus and Jiangxigraptus vagus biozones can be recognized. Some intervals are poorly documented by their respective graptolite faunas or show extensive post-depositional tectonic deformation. The Nemagraptus gracilis Biozone of earliest Sandbian age cannot be positively identified, even though fragments of Nemagraptus have been discovered in the uppermost part of the Almelund Shale below the Fågelsång Phosphorite Bed.

Upper Ordovician (Sandbian) conodonts from the Hoedongri Formation of western Jeongseon, Korea

Five sections in western Jeongseon-eastern Pyeongchang provide a relatively complete composite section of carbonate platform facies through the upper part of the Hoedongri Formation. A total of 29 samples (125 kg) yielded 669 relatively well-preserved conodont specimens, which are classified into 16 species representing 10 genera. The fauna is dominated by Panderodus gracilis (Branson and Mehl) (55%), which generally is believed to have been pelagic and eurytopic, and comprises characteristic elements of North China faunal affinities. Other taxa include Aphelognathus solidum Pei, Belodina sp., Eoligonodina prima (Branson and Mehl), Erismodus asymmetricus (Branson and Mehl), E. quadridactylus (Stauffer), Plectodina aculeata (Stauffer), P. alatheta An, Tasmanognathus careyi Burrett, and T. sishuiensis Zhang. This assemblage was assigned to the Tasmanognathus sishuiensis-Erismodus asymmetricus Zone herein. The interval of the zone is between the first and last occurrences of the eponymous species. The lower limit of the zone is unclear due to the absence of conodont data from underlying dolomitic limestone beds. The T. sishuiensis-E. asymmetricus Zone is the youngest conodont zone in the Taebaeksan Basin, Korea and was correlated to the ‘upper fauna’ of the Yeongheung Formation in Yeongwol, Korea, to the Belodina compressa-Microcoelodus symmetricus Zone in Shandong, to the T. sishuiensis-Erismodus typus Zone in Gansu, and to the T. sishuiensis Zone in the Ordos Basin, North China, representing the interior platform and slope facies of Sandbian age. Based on the recent recognition of the Aurilobodus serratus Zone and T. sishuiensis-E. asymmetricus Zone, the Hoedongri Formation was assigned to the Middle Ordovician to early Late Ordovician (Darriwilian, D3 to Sandbian, Sa2).

A new age model for the Ordovician (Sandbian) K-bentonites in Oslo, Norway

During the Late Ordovician, large explosive volcanic eruptions deposited worldwide K-bentonites, including the Millbrig and Deicke K-bentonites in North America and the Kinnekulle K-bentonite in Scandinavia. We have studied a classical locality in Oslo containing one of the most complete sections of K-bentonites in Europe.In a 53 m section of Sandbian age, we discovered 33 individual K-bentonite beds, the most notable beds being the Kinnekulle and the upper Grimstorp K-bentonite. Magnetic susceptibility (MS) measurements on two intervals show significant periodicity peaks interpreted as Milankovitch cycles and thus astronomically forced changes in sediment supply and composition. These cycles fit remarkably well with both the expected Milankovitch periodicities for the Ordovician as well as the radiometric ages presented in this study and may represent one of the most convincing demonstrations of Milankovitch cycles from the lower Paleozoic so far. Five of the K-bentonites have been dated by high-precision chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) U-Pb zircon geochronology, where the Kinnekulle K-bentonite gives an age of 454.06 ± 0.43 Ma. We have integrated the new data and calculated an age model showing the sedimentation rates through the section and thereby the ages of each of the 33 K-bentonites. Using the age model, we further present a new age for the Sandbian-Katian stage boundary. The section in Oslo provides the highest resolution window into the Upper Ordovician K-bentonite succession so far and helps shed more light on the chronology of one of the most intense volcanic periods of the Paleozoic and the relationship with the global carbon cycle changes that followed.

Climatic and oceanic changes during the Middle-Late Ordovician transition in the Tarim Basin, NW China and implications for the Great Ordovician Biodiversification Event

The Middle-Late Ordovician transition (Darriwilian to Sandbian Age) witnessed a major pulse of the Great Ordovician Biodiversification Event (GOBE) and distinctive oceanic geochemical fluctuations, such as coeval negative C and Sr isotope excursions. In this study, investigations into geochemical variations, notably the Hg abundance (or Hg/TOC), have been carried upon the organic-rich black shale of the Middle-Upper Ordovician Saergan Formation to unravel the causes of this pulse. Based on these data, three phases were identified. Phase 1 (0 to 3 m) is characterized by rising Hg/TOC (up to 138 ppb/wt%) and Ti/Al values as well as high CIAcorr (corrected chemical index of alteration) values (68.9–72.3) with negligible enrichment of redox sensitive elements (RSE) and nutrient elements (e.g. U ≤ 5.2 ppm, V ≤ 153 ppm, Mo ≤ 1.8 ppm, P2O5 ≤ 0.2%), suggesting intensified volcanism, which could have emitted significant amounts of greenhouse gases, thereby leading to climate warming. In contrast, Phase 2 (3 to 11 m) is characterized by decreasing Hg/TOC and Ti/Al ratios, relatively low though slightly fluctuating CIAcorr values, generally depleted in RSE (except moderately enriched U up to 14.6 ppm) and increased P/Al and Ba/Al ratios, implying weakening volcanic activity and subsequent climate cooling and the potential for improved seawater ventilation as a result of oceanic upwelling. Phase 3 (Sandbian Age: 11–13 m) witnessed continuous decrease in Hg/TOC ratio, an increase in Ti/Al and CIAcorr values, fairly low values of RSE enrichment and P/Al and Ba/Al ratios, indicating recurrent climate warming, and the potential for slowed oceanic circulation and attenuated upwelling of nutrient-rich deep waters onto the shallow shelf. These changes could have diminished bioproductivity and organic output onto the seafloor. This study offers insights into volcanic-climatic-oceanic interactions during a major pulse of the GOBE around the Middle-Late Ordovician transition while black shales were extensively deposited.

Middle–Late Ordovician chitinozoans from the Yichang area, South China

Chitinozoans from the Miaopo Formation (topmost Middle to lower Upper Ordovician) at Jieling, northern Yichang, western Hubei, were systematically studied, and 43 species of 16 genera were identified, which substantially increases the chitinozoan diversity of this particular time interval of the South China palaeoplate. Several key chitinozoan species from North Gondwana (e.g., Lagenochitina ponceti Rauscher) and Baltica (e.g., Laufeldochitina stentor (Eisenack) and Cyathochitina sebyensis Grahn) are reported for the first time in China. The chitinozoans of this formation are of late Darriwilian–early Sandbian age, and they have mixed North Gondwana and Baltica palaeogeographic affinities. The recognition of L. stentor, Armoricochitinagranulifera and C. sebyensis guarantees a better biostratigraphic correlation between South China and Baltica. Most of the formation, except for its topmost part, is assigned to the L. stentor Biozone, which can be further subdivided into two subzones: the Cyathochitina megacalix sp. nov. Subzone (lower) and the A. granulifera Subzone (upper). Three new species are formally described: C. megacalix sp. nov., Cyathochitina raricostata sp. nov. and Eisenackitina tenuis sp. nov.

The Ordovician genusPygodus(conodont) in the Cuyania Terrane, Argentina

AbstractThis contribution deals with the record of the Ordovician genusPygodusin Cuyania, Argentina. Several classical sections have been sampled for conodonts in the Precordillera and the San Rafael Block, involving diverse sedimentary deposits: coarse clastic rocks with carbonate cement, carbonate beds intercalated in fine clastic deposits, green shale, and black carbonate deposits. The recovered species of this genus arePygodus lunnensisZhang,P. anitaeBergström,P. serra(Hadding),P. protoanserinusZhang andP. anserinusLamont & Lindström. These key conodonts indicate middle to upper Darriwilian – lower Sandbian age for the bearing strata. The speciesP. protoanserinusis recorded for the first time from the Precordillera. Detailed observations were made on specimens ofP. anitae,P. lunnensisandP. protoanserinus; the two last species are described for the first time from Cuyania.

The Earliest Giant Osprioneides Borings from the Sandbian (Late Ordovician) of Estonia

The earliest Osprioneides kampto borings were found in bryozoan colonies of Sandbian age from northern Estonia (Baltica). The Ordovician was a time of great increase in the quantities of hard substrate removed by single trace makers. Increased predation pressure was most likely the driving force behind the infaunalization of larger invertebrates such as the Osprioneides trace makers in the Ordovician. It is possible that the Osprioneides borer originated in Baltica or in other paleocontinents outside of North America.

Late Ordovician Ostracods of the Girvan District, South-West Scotland

The Late Ordovician ostracod fauna recorded from the Girvan district, south-west Scotland, comprises 54 species from 26 genera and 15 families, but includes 22 species described in open nomenclature and a further 17 that are considered as nomina dubia. The ostracods include representatives of the podocope suborders Palaeocopina, Binodicopina, Leiocopina and Metacopina, and the new genera and species Danemestrinus scotus n. gen. et sp., Leperditella girvanensis n. sp. and Krausella jonesiana n. sp. are described. The fauna includes several species that allow inter-continental correlation with the Late Ordovician succession of North America, including the Sandbian species Eurychilina sunbloodensis, Balticella deckeri, Baltonotella parsispinosa and Hippula ventrospinosa. The Katian species Kinnekullea comma has correlative value between Scotland, Ireland, England and the East Baltic. Biogeographically, the Girvan ostracod fauna of Sandbian age shows strong affinities at species-level with the fauna of palaeocontinental Laurentia, but from the early Katian onwards there are species level links with the Baltic region, and some common taxa at generic and species-level with palaeocontinental Avalonia.

Biotic response to explosive volcanism: Ostracod recovery after Ordovician ash-falls

The impact of two Ordovician ash-falls of different intensities was studied in order to determine the recovery patterns of benthic ostracods. The studied sections are of Sandbian age in NW Estonia: at Põõsaspea, the Kinnekulle K-bentonite (~40cm, derived from a major volcanic event) and at Ristna, the Grimstorp bentonite (~6cm). In Põõsaspea, important faunal changes are observed: the three pre-crisis dominant species (i.e. Tetrada memorabilis, Steusloffina? sp. nov. and Olbianella braderupensis) were not recovered above the bentonite and at least two of them became extinct. The post-crisis ecosystem shows strong perturbations of diversity and abundance for a long period of time. In Ristna the impact of the ash-fall is less dramatic: all of the dominant pre-crisis species survived, although some changes in abundance and diversity are observed. These results show that significant ash-falls lead to marked rearrangement of assemblages and extinction of some taxa while less prominent volcanic episodes only result in temporary changes in the assemblage structure. In both cases, recovery follows several steps:–Post-event ecosystem with ‘survival faunas’ (very low abundance; low diversity); one/two species (opportunistic taxa?; e.g. Sigmoopsis rostrata, Circulinella nuda) dominate the assemblage.–Early stages of recolonization with ‘recovery faunas’ (increasing abundance and diversity; recolonization by pre-event and immigrant species).–After a short ‘disturbance period’, return to ‘climax assemblages’ with specialized taxa (high abundance; high diversity).Although assemblages recovered rapidly after the crises, the recovery periods still seem much longer than observed in Recent foraminiferal assemblages. Causal links between the volcanic events and subsequent diversifications could not be demonstrated.